1. Field of the Invention
The present invention relates to a steering system for vehicles. More particularly, the invention relates to an improvement in a steering system for a vehicle with front and rear wheels, which steering system permits both the front wheels and the rear wheels to be steered.
2. Description of Relevant Art
There have been proposed by the present applicant a variety of steering systems for a vehicle with front and rear wheels, which steering systems permit the front and rear wheels to be concurrently steered, while varying the steered angle ratio therebetween in accordance with the steering angle of a steering wheel.
In U.S. patent application Ser. No. 407,421 filed Aug. 12, 1982, there is described an example of such steering systems consisting of a steering wheel, a front steering sub-system for steering the front wheels in accordance with the steering angle of the steering wheel, and a rear steering sub-system for steering the rear wheels in accordance with the steering angle of the steering wheel. The front steering sub-system includes a steering gearing of a rack and pinion type composed of a drive pinion interlocked to be rotatable with the steering wheel, a rack shaft having a first rack engaged with the drive pinion and a second rack separated from the first rack, and a driven pinion engaged with the second rack. The rear steering sub-system includes an input shaft interlinked with the driven pinion, an off-centered pin secured to one end of the input shaft, a pair of rear tie-rods adapted eacg respectively to turn either of the rear wheels, and a joint member relatively pivotably connected to the off-centered pin and both of the rear tie-rods, the joint member being arranged to be movable vertically and transversely of the vehicle in accordance with the crank motion of the off-centered pin, thereby rendering the steered angle ratio between the front and rear wheels variable according to the steering angle of the steering wheel.
According to such exemplary steering system, the rear wheels are permitted to be steered in the same direction as the front wheels for relatively small steering angles of the steering wheel and in the opposite direction thereto for relatively large steering angles of the steering wheel, thus providing the vehicle with favorable maneuverability characteristics when travelling at relatively high speeds, as well as favorable vehicle turning characteristics due to relatively small turning radii possible with large steering angles such as when executing a U-turn or when steering in and out of a parking space.
However, in the exemplified steering system, the joint member has a vertically extending portion loose-fitted at the upper part thereof on the off-centered pin and connected at the lower part thereof to each of the rear tie-rods and is disposed under a floor panel of a body of the vehicle, thus being necessarily restricted in the space for arrangement in the vertical direction, which leads to a desideratum for a favorable joint member designed to have relatively small vertical dimensions and sufficiently designed for the pivotal connection with the rear tie-rods in addition to being arranged thereabout to be as compact as possible.
Moreover, in the steering system in question, the drive and driven pinions, which are accommodated in a steering gear box, are engaged with the first and second racks, respectively, forming respective predetermined angles therebetween which are different from each other, necessarily due to the structure of the vehicle, when axially viewed from either end of the rack shaft, so that the adjustment for respective engagement relations of these two rack and pinion mechanisms is considerably difficult and must be made independently of the bearing adjustment of the rack shaft adjustment service of the steering gear box is thus rendered extremely troublesome, which leads to another desideratum i.e., for a favorable steering gearing with simplified fabrication and maintenance.
The present invention has been achieved to improve a steering system for vehicles, which is already proposed by the applicant, by fulfilling the aforesaid desiderata.